B freeman



Feb. 21, 1956 M. B. FREEMAN 2,735,625

APPARATUS AND METHOD FOR PROCESSING ASPHALT Filed May 12, 1952 25 Sheets-Sheet l Feb. 21, 1956 M. B; PREEMAN 2,735,625

APPARATUS AND METHOD FOR PROCESSING ASPHALT Filed May 12, 1952 3 Sheets-Sheet 2 .Z/Vl/E/VTOR MARI NV 5. PAEEMA/V Feb. 21, 1956 FREEMAN 2,735,625

APPARATUS AND METHOD FOR PROCESSING ASPHALT Filed May 12, 1952 3 Sheets-Sheet 3 APPARATUS AND METHOD. FOR PROCESSING ASPHALT Marvin B. Preeman, Los Angeles, Calif., assignor to'Standard Steel Corporation, Los Angeles, 'Calif., a corporation of California Application May 12, 1952, Seriai'No. 287,433

17 Claims. -(Cl. 241-18) ing roads has been to use hot asphalt mixes in which theasphalt content is in heated liquid form. The general object of the present invention is to make available to the industry the special advantages of cold asphalt mixes in which the asphalt content is in dry form.

Asphalt is a solid at moderate temperatures, more or less tacky and molten at the higher temperatures of hot summer or desert weather and at somewhat higher temperatures becomes sufliciently liquid for blending with aggregate to produce the familiar hot paving mix. Certain problems in the large-scale production of hot mixes arise from the necessity of applying heat'and, more important, arise from the tendency of the material to cling to surfaces in hardened masses. The mostserious disadvantage in the use of hot mixes, however, is that sincethe mix sets or hardens when it cools,it must be'used promptly. It cannot be stored, or even permitted to cool in any kind of conveyance or container, and, therefore, too-often must be prepared in uneconomically small batches.

It has long been known that these disadvantages and limitations may be avoided by using cold mixes in which the asphalt in powder form is intermixed with the aggregate together with a suitable oil. No heat is required; the material does not tend to build up and set-to form hard accumulations'on the surfaces of the processing apparatus; and the finished mix may be stored indefinitely for use as desired. Obviously, cold-mix methods are basically less expensive and can be used-in many situations where hot-mix methods would not be practical.

It so happens, however, that the properties of asphalt in powdered form give rise to new problems which have heretoforeprevented successful use of cold mixes involving powdered asphalts. Various unsuccessful attempts have been made to solve these problems.

Powdered asphalt is exceedingly 'difiicult to handle. If only slightly heated, ittends to become tacky and if mildly heated while stored in a container, "thepowder will harden into a solid mass. If the powdered'asphalt' fully protected from heatis stored in ahopper for releaseby the use of valves or'gates, the powder either'do'es not'fiow at all because it forms arches ore'ls'e itsuddenly behaves much like a liquid. Thus, the powder mass does not respond uniformly to the operation'of a valve or gate and, therefore, cannot be controlled to an acceptable degree. The use of storage hoppers is notpractical, furthermore, because in time an undisturbed mass of vpowder'terids to cake and will certainly do so in 'hot weather.

Since the properties of powdcred asphalt preclude'either bulk shipment or bulk storage, it would be logical to ship and store the asphalt in the familiar lump'form'and 'then togrinditto powder'as-requiredby'the mixerinahe final stage of blending-the powder-into 'the aggregate and oil. it would be 'logioal,furthermore,to-placethe grindnited States Patent 2,735,625 Patented Feb. 21, 1956 ing apparatus immediately above the mixer and simply let the powdered asphalt drop into the mixer as fast as it is produced. Such a simple solution is precluded how ever by certainpract-ical considerations that must dominate in the design of an efiicient asphalt plant and, especially, a unit that can be dismantled for movement from'one location to another in the field. The dominating consideration is the handling of the aggregate.

To achieve a high rate of production it is essential that the aggregate be stored directly above the mixer and fed to the mixer in downward streams directed transverselyof the axis of the mixing apparatus. The direct drop of the bulk of the material in this way cuts handling time to the minimum and the transverse direction reduces stratification of the materials in the mixer and thus minimizes the time required for complete blending of the materials. With the aggregates handled in this way, the mixer operation may be reduced to as short a time period as one minute or less; whereas changing this arrangement to grind asphalt immediately above the mixer greatly complicates the handling of aggregates and, at best, would drop production to an uneconomical level.

Thefinal problem to be solved, then, is to convey the powdered asphalt a few-feet from a grinder to the mixer. It is tobe borne in mind that the grinding operation itself generates heat and thus increases the difficulty of handling the heat-sensitive powder. It has been found that the use of a screw conveyor, or any other type of mechanical conveyor, for moving the powdered asphalt direct from the grinder is. impractical because the residual heat causes the particles to adhere and accumulate rapidly on the exposed conveyor surfaces.

One serious 'atter'npt'to solve this problem in the past was to grind the asphalt at ground level and blow the product to the mixer through a conveyor duct, on the theory that the air used for conveyance would cool the powder'and keep the powder moving. It was necessary to add a cyclone chamber tokeep the .air stream from carrying toomuch of the dust into the atmosphere. This attempt failedbecause the powdered material formed arches orbridg'es to clo'g'up both the duct and the cyclone chamber, the conveying apparatus becoming inoperative in a short period.

A special object of the present invention is to solve this p'articular'handling problem. This object is attained by combining the use of an air stream with the use of mechanical means for conveying the powdered asphalt. The underlying concept is that the air stream will provide necessaryfactors that are lacking in a wholly mechanical system, and, conversely, mechanical operation meets the deficienciesof wholly pneumatic conveyors. Thus, the air stream cools the powder as well as conveys a substantial portion of the material and in addition prevents powder accumulation on'the moving surfaces of the conveyor; on the other hand, the accompanying mechanical action prevents'caking and the formation of arches of powder that 'makepneumatic systems inoperative.

An important'featureis the further concept of blowing air into the mill that grinds the powder, the purpose being to precool 'the material and to provide sufficient heat dissipation "to minimize the heating effect of the grinding operation. The combination of at least one air jetin the mill with at least one air jet in the conveyor from the mill will stand the tests of continuous operation in the heat of summer weather.

While various mechanical conveyor arrangements may beused, a'screw conveyor is preferred and certain objects of the preferred practice'o f the invention pertain to the 'use of such-a screw conveyor, as will be apparent. One of these objects is to provide such an arrangement in which the'force of the air stream is reduced or dissipated -:befor'e the'material reaches the end of the conveyor. As

a result, the powder simply drops into the mixer without a portion of the powder being blown into the atmosphere.

Other specific objects relate to the timing and coordination of the grinding operation with respect to the operation of the mixer. With a mill large enough to match the short operating cycle of the mixer, the lump material must be fed to the mill at a controlled rate and the powdered product must be carried rapidly away from the mill to the mixer. For this purpose a screw conveyor is added to feed the mill and both conveyors are suitably regulated as well as coordinated with the operating cycle of the mixer.

A further object of the invention is to combine these various concepts in a compact, high-production field plant which may be readily moved from one location to another.

The various objects and advantages of the invention will be readily understood from the following detailed description along with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative,

Fig. l is a front elevation of the presently preferred embodiment of the invention;

Fig. 2 is a fragmentary front elevation of the grinder and the conveyor therefrom, the view being on a somewhat enlarged scale;

Fig. 3 is a view in side elevation and partly in section taken as indicated by the line 33 of Fig. 1;

Fig. 4 is a similar view taken from the opposite side as indicated by the line 4-4 of Fig. 1;

. Fig. 5 is an enlarged view partly in elevation and partly in section of the conveyor shown in Fig. 2;

Fig. 6 is a plan view of the same conveyor shown apart from the grinder;

Fig. 7 is a transverse section taken as indicated by the line 77 of Fig. 5; i

Fig. 8 is an end view of the conveyor partly in section as indicated by the line 8-8 of Fig. 5; and

Fig. 9 is a similar view at the discharge end of the conveyor taken as indicated by the line 99 of Fig. 5.

The presently preferred embodiment of the invention is in the form of an asphalt plant for use in the field. The apparatus is releasably fitted together in sections so that the plant may be readily erected or dismantled with the aid of a crane to permit use of the plant at difierent locations.

As shown in Figs. 1, 2 and 4, the frame structure of the plant includes four legs 10 to form a driveway under the apparatus for trucks so that the finished asphalt mix may be loaded by gravity for conveyance to points of use. In preparation for erection of the plant, concrete foundation blocks 11 are provided for the legs 10 on opposite sides of the driveway and concrete lined pits 12 are provided on opposite sides of the foundation.

The four legs support a platform 15 for the operator with various controls within convenient reach. Well above the platform 15 is suitable storage means for the aggregate and lump asphalt. In the particular construction shown, an elevated storage bin generally designated 16 is divided into a compartment 17 for lump asphalt and three compartments 18, 19 and 20 for aggregate. These three compartments may contain, for example, coarse gravel, pea-sized gravel, and sand, respectively.

Aggregate delivered to the plant is dumped into the boot 24 of an elevator 25 driven by a suitable motor 26, which elevator has a three-way chute 27 for discharging the material into the bin compartments 18, 19 and 20 selectively. If a first bottom gate in the chute 27 controlled by a lever 28 is opened, the material in the chute drops into the bin compartment 20; if the first bottom gate is closed and a second bottom gate controlled by a lever 29 is open, the material in the chute 27 discharges into the bin compartment 19; and if both of these bottom gates are closed, the material in the chute 27 continues to the lower end of the chute 27 and drops through a bottom opening of the chute into the bin compartment 18. Suitable chains 30 extending downward to the region of the platform 15 permit remote control of the two gate levers 28 and 29.

' hopper 33 for discharge of the hopper content into a suitable mixer 37 in which the final blending operation is performed to produce the final cold asphalt mix. The mixer 37 which has a dust housing 38 and is driven by a motor 39 is of a well-known type having teeth or paddles. The mixer is provided with a suitable discharge gate (not shown) on its under side which is operated by compressed air under control of the operator on the platform 15.

One of the ingredients of the final mix is a suitable flux oil which may be supplied and introduced into the mixer 37 in any suitable manner. For this purpose, the oil may be stored at or below ground level and boosted upward through a pipe 40 (Fig. 4) by a suitable continuously running pump (not shown). A three-way valve (not shown) at a location convenient for the operator may be turned to one position for recirculating the oil back to storage and may be turned to a second position to route the'oil to a pipe 41 discharging into a weigh bucket 42 which is part of a suitable scale 43. A pump 45 (Fig. 4) has an intake pipe 46 extending into the weigh bucket 42 and a discharge pipe 47 which leads to a suitable spray pipe (not shown) in the mixer 37. The pump 45 is operated by a suitable motor 48 which the operator may start by a push button 49 (Fig. 1). A suitable switch (not shown) operated by the scale arm of scale 43 stops the motor 48 automatically when the weigh bucket is emptied.

Lump asphalt of random size as large as six inches in cross dimension is delivered to a pre-breaker 50 on the boot of an elevator 51. The pro-breaker and the elevator are driven by motors 52 and 53, respectively, the two motor controls being interlocked to run the prebreaker and elevator simultaneously. The pre-breaker reduces the size of the asphalt lumps to the order of two inches maximum dimension and the elevator delivers the initially processed lump asphalt to the previously mentioned storage bin compartment 17. 4

As best shown in Fig. 3, lump asphalt is taken from the storage bin compartment 17 to a suitable weigh hopper 57 by a screw type conveyor 58 driven by a suitable motor 59. The motor 59 is started by a push button 60 and is stopped automatically by a suitable cut-off switch when the weight of the asphalt in the weigh hopper 57 reaches the desired magnitude. The asphalt weigh hopper 57 is part of a suitable scale-61.

When the operator shifts the previously mentioned control lever (not shown) to dump the content of the aggregate weigh hopper 33, a suitable switch (not shown) responsive to this fourth lever, starts the motor 64 of a second screw conveyor 65 that is carried by the asphalt weigh hopper 57. This second screw conveyor 65 delivers the lump asphalt at a suitably regulated rate to a hammer mill 66 that grinds the asphalt to powder. The mill 66 is driven continuously by a suitable motor 67 (Fig. 3). The motor 64 for the screw conveyor 65 is stopped automatically by switch means (not shown) responsive to the upward movement of the weigh hopper 57 to its empty level. The mill 66 discharges the powdered asphalt into a third screw-type conveyor generally designated 68 that is operated continuously by a motor 69 to carry material from the mill to the mixer 37.

The construction of the screw conveyor 68 and its cooperation with the hammer mill 66, which are the 5 important features of the invention, may be understood with reference to Figs. .5 to 9 of the drawings.

The conveyor 63 has a screw comprising a spiral blade 70 on a longitudinal shaft 71 that is journalled in two suitable bearings 72 and is driven by a chain 73 and sprocket 74. The two bearings 72 are mounted on opposite ends of a conveyor housing comprising a receiving hopper 77 and a cylindrical duct 78 extending therefrom coaxially of the shaft 71.

As may be seen in Figs. 5, 6 and 7, the receiving hopper 77 conforms in plan to the configuration of the bottom of the hammer mill 66 and is provided with a flange 8%) to match a corresponding flange 81 of the hammer mill for attachment thereto by suitable bolts 82. The end wall 83 of the hopper 77 has an opening closed by a removable plate 84 that carries one of the two shaft bearings 72. This end wall 83 and the two side walls 85 of the receiving hopper 77 are in the same planes of the corresponding walls of the hammer mill. The bottom wall 86 of the receiving hopper is in the shape of a trough having a bottom curvature conforming to the circumference of the spiral conveyor blade 70 and has a curved clean-out door-87 normally held closed by screws and thumb nuts 83.

The cylindrical duct 78, is, in effect, a longitudinal extension of the receiving hopper 77 and conforms to the circumference of the spiral blade 70. The outer end of the cylindrical duct '78 is cut away on its under half to form a discharge opening 90 and the outer end carries a removable end wall 91. As may be seen in Fig. 5, the outer end of the cylindrical duct 78 extends inside the dust housing 38 above the mixer 37.

The most important feature of the conveyor 68 is the manner in which an air stream is used therein and, preferably, an air stream is also introduced into the hammer mill 66. For this purpose, a supply pipe 95 (Fig. 6) for compressed air is connected to a nozzle 96 in the removable plate 84 on the end wall 83 of the receiving hopper 77, as shown in Figs. 5 and 6, and a branch 97 from the supply pipe extends upward to the hammer mill, as shown in Fig. 2. The branch pipe 97 is connected to a second nozzle directed into the interior of the hammer mill just below the usual perforated member in the mill (not shown) through which the powdered product passes downward into thereceiving hopper 77.

It is contemplated that the powdered material from the mill will be moved through the conveyor 68 partially by the mechanical action of the spiral blade 70 and partially by entrainment in the air stream from the nozzle 96. To make such cooperation between the spiral blade and the air stream possible, at least one longitudinal air passage will be formed through the conveyor 68 in any suitable manner. In the presently preferred practice of the invention, there are three air passages through the screw conveyor 68 formed by three longitudinal series of windows 100 out in the material of the spiral blade 7:). Thus, in effect, the spiral blade is converted into a ribbon-type conveyor in which the ribbon is supported from the shaft 71 by spoke portions 101, the spaces between the spokes providing the required passages for air flow. The nozzle 96 is positioned above the shaft 71 to register with the three longitudinal series of windows -190 as the three series rotate about the axis of the shaft. Thus, each of the three longitudinal air passages is subjected to the blast of air in succession as the spiral blade rotates.

The air introduced into the "hammer mill 66 tendsto precool the lump material in addition to dissipating the heat generated by the pulverizing action. The air blown into the mill also solves the problem of eliminating the tendency of the powdered material to clog the perforations through which the powdered material drops from the mill to the receiving hopper 77 of the conveyor. This problem is solved in part, of course, by heat dissipation 6 reducing the tackiness of the powdered product, but ai further factor is the effect of the air streamin exert ing pressure to dislodge material from the perforations. The air stream from the mill is directed downward into the conveyor to urge material into the region to be picked up by the air stream from the conveyor nozzle 96.

The air from the conveyor nozzle 96 not only entrains powder to carry powder through the air passages to the outer end of the cylindrical duct 78, but also'further dissipates heat generated by the grinding process and thereby reduces the tendency of the powdered asphalt to adhere to the metal surfaces inside the conveyor 68. A further function of the air stream through the conveyor is to dislodge material adhering'to the spiral blade and, in this regard, it will be noted that all the surfaces adjacent the three longitudinal air passages are periodically subjected to the blast of air. Thus, the air stream not only lessens the burden of the spiral blade 'by conveying a portion of the powder but also acts on the spiral blade to keep deposits from forming thereon to an inoperative extent; and, on the other hand, the spiral blade not only reduces the burden of theair stream in conveying the powdered product but also continually mechanically destroys any tendency for the powder to bridge or arch across the air passages.

-It has been found that with the nozzle at one end of the conveyor, as described, the air stream may have sufficient force 'to serve the purposes in mind and yet fall off in force at the discharge end of the conveyor to such degree that the powder drops straight from the discharge opening 99 into the mixer 37 without being blown into the atmosphere. The air stream drops in force partly because of the baffle action of the rotating spiral blade 70 and'partly'because the volume and configuration of the interior of the conveyor 68is such that the air stream is permitted to expand toward the discharge end of the conveyor. The force of "the air-stream maybe permitted to diminish in this manner at the discharge end of the conveyor without sacrificing efilciency because the powdered materialis progressively cooled to reduce its tendency to adhere to surfaces as the material reaches the discharge opening and also because the conveyor is open at the bottom at the discharge opening to permit the material to drop freely away from the rotating blade.

A further feature of the invention with reference to the problem of handling material in the conveyor 68 stems from the operating cycle of the apparatus which, as willbe explained, requires'passage of material through the hammer mill and conveyor only intermittently. Thus, the mill and conveyor are, in effect, precooled in preparation for each periodic operation, the precooling being accomplished not only by the blasts of introduced air but also by the movement of the operating metal surfaces relative to the enclosed air. In addition, the idle rotation of the continuously operating spiral blade of the conveyor between conveying operations tends to dislodge residual material adhering to the metal surfaces.

The manner in which the operating cycle'of the apparatus is carried out may be readily understood from the foregoing description. The aggregate from the three bin compartments 18, 19 and 20 is weighed into the hopper 33 of the scale by manipulation of the levers 34. This weighing operation is carried out while the preceding batch is in process in the mixer 37. In this same time period, the operator manipulates the previously mentioned three-way valve to discharge the desired quantity of oil into the weigh bucket 42. The operator also has time during the mixing of the preceding batch to weigh'out the quantity of lump asphalt required for a batch since he need only press the push button 60. The push button starts the conveyor 58 and the conveyor is automatically stopped when the correct weight is reached.

When the preceding batch in the mixer 37 has been processed for the required period of time, the operator opens the air-controlled discharge gate to empty the mixer and then closes the gate in preparation for depositing a new batch of materials in the mixer. To charge the mixer with the new batch, the operator throws a lever to empty the aggregate of the weighing hopper 33 into the mixer and, as previously explained, the lever operates a switch to start the conveyor 65. The operator also presses push button 49 to cause oil from the weigh bucket 42 to be sprayed under pressure into the mixer. As fast as the asphalt in lump form is ground by the mill into powder the asphalt drops into the screw conveyor 68 for conveyance to the mixer as heretofore described.

It may be readily understood how the described appa ratus may easily process as many as seventy-five or more tons of the cold asphalt mix per hour.

The foregoing description in detal of a preferred practice of the invention will suggest to those skilled in the art various changes, substitutions and other departures from the disclosure that properly lie within the scope and spirit of the appended claims.

I claim as my invention:

1. A method of handling asphalt to supply an asphalt mixer, including the steps of: conveying the asphalt in lump form to a point adjacent the mixer; grinding the asphalt to powder form at said point; mechanically conveying the powdered asphalt along a path from said point to the mixer; and blowing air along said path to dissipate heat created by the grinding operation and to facilitate the movement of the powdered asphalt along the path.

2. A method of handling asphalt to supply an asphalt mixer, characterized by the use of a mill near the mixer and a screw conveyor fed from the mill for delivery to the mixer, said method including the steps of: conveying the asphalt in lump form to said mill to be ground thereby into powder and to be fed therefrom to said conveyor; blowing air into said mill to dissipate heat generated therein; and blowing air into said conveyor both for further dissipation of the generated heat and for facilitating movement of the powder through the screw conveyor.

3. A method as set forth in claim 2 in which the lump material is fed to the mill and conveyor periodically for periodic operation with the air blowing into the mill and conveyor continuously to precool mill and. conveyor prior to each period of operation.

4. A method as set forth in claim 3 in which the conveyor is operated continuously for cooling and selfcleaning between the periodic operations.

5. A method of handling asphalt to supply an asphalt mix for use in the field, including the steps of: conveying the asphalt in lump form to the field; grinding the lump asphalt to powder form in the field; feeding the asphalt powder to a screw conveyor leading to a mixer; and blowing air into said conveyor in the direction of mate rial travel therethrough both to cool the asphalt and to facilitate movement of the powder through the conveyor.

6. A method as set forth in claim 5 in which the lump material is ground and delivered to the conveyor periodically but air is blown into the conveyor continuously thereby precooling the conveyor for each periodic operation.

7. A method as set forth in claim 6 in which the screw conveyor is run continuously for cooling and self-cleaning between the periodic operations.

8. A method of handling asphalt to supply an asphalt mix for use in the field, including the steps of: conveying I 8 through said air passage in the direction of material travel both to cool the powder and to facilitate movement of the powder.

9. In an apparatus for producing mixed asphalt, the combination of: a mixer; means to supply said mixer with aggregate; a mill to grind lump asphalt to powdered form, said mill being adjacent said mixer conveying means to deliver the powdered asphalt to the mixer, including means to discharge cooling air into the conveying means in a direction toward the mixer; and means to supply lump asphalt to said mill.

10. In an apparatus for producing mixed asphalt, the combination of: a plurality of storage compartments for aggregate; a storage compartment for lump asphalt; a mixer; means to deliver predetermined quantities of aggregate from said plurality of compartments to said mixer; a mill to grind lump asphalt to powder; means to deliver a predetermined quantity of lump asphalt from said stor age compartment to said mill; and means to deliver the powdered asphalt from said mill to said mixer, including means to blow cooling air through said powder delivery means.

11. A combination as set forth in claim 10 which includes means to blow cooling air through both said mill and said powder delivery means in the direction of travel of the material. I

12. In an apparatus for producing mixed asphalt, the combination of: a plurality of compartments for storing aggregate; a compartment for storing lump asphalt; a mixer; means to deliver predetermined quantities of aggregate from said plurality of compartments to said mixer; a mill to grind lump asphalt to powder; means to deliver a predetermined quantity of lump asphalt from said storage compartment to said mill; an enclosed mechanical-type conveyor to deliver the powdered asphalt from said mill to said mixer, said conveyor having at least one longitudinal air passage therethrough; and means to direct a jet of air into said passage in the direction of travel of the material to entrain a portion of the powdered asphalt and to remove accumulations of the asphalt powder from the surfaces of the conveyor.

13. A combination as set forth in claim 12 which includes means to direct air into said mill to dissipate heat generated therein.

14. A combination as set forth in claim 12 in which said conveyor is a screw-type conveyor with the longitudinal passage therethrough inside the circumference of the screw.

15. A combination as set forth in claim 12 in which said conveyor includes a screw blade with a series of offcenter apertures therein aligned longitudinally of the conveyor and in which said jet means is positioned oitcenter to register with said series of apertures.

16. A combination as set forth in claim 15 in which there is a plurality of series of longitudinally aligned apertures in the screw blade positioned to register in succession with the jet of air.

' 17. A combination as set forth in claim 16 which includes means to introduce a stream of air also into said mill.

References Cited in the file of this patent UNITED STATES PATENTS 1,138,397 Nesetril May 4, 1915 1,199,621 Sheppard Sept. 26, 1916 1,953,091 Westberg Apr. 3, 1934 1,965,881 Clark July 10, 1934 2,591,721 Poulsen Apr. 8, 1952 

1. A METHOD OF HANDLING ASPHALT TO SUPPLY AN ASPHALT MIXER, INCLUDING THE STEPS OF: CONVEYING THE ASPHALT IN LUMP FORM TO A POINT ADJACENT THE MIXER; GRINDING THE ASPHALT TO POWDER FROM AT SAID POINT; MECHANICALLY CONVEYING THE POWDERED ASPHALT ALONG A PATH FROM SAID POINT TO THE MIXER; AND BLOWING AIR ALONG SAID PATH TO DISSIPATE HEAT CREATED BY THE GRINDING OPERATION AND TO FACILITATE THE MOVEMENT OF THE POWDERED ASPHALT ALONG THE PATH. 